The use of diet diaries in general dental practice in England.

OBJECTIVES: Diet diaries are recommended as a tool to support behaviour change in dental patients at high risk of dental diseases. However, little is known about their use in dental practice. This study aimed to investigate whether and how general dental practitioners (GDPs) use diet diaries and identify factors which influence their use. METHODS: A postal questionnaire was sent to a stratified random sample of general dental practitioners. The questionnaire asked about demographic and professional characteristics of the GDPs and their practices regarding diet advice, collection of dietary information, diet diaries usage (e.g. frequency, considerations and barriers), and interpretation of diet diaries. Descriptive, bivariate and multivariate analyses were conducted. RESULTS: From 972 eligible GDP participants, 250 (26%) responses were received. Whilst almost all of these GDPs reported giving diet advice to patients routinely, and 40% reported also referring to dental care professionals in the practice to deliver dietary advice, only 28% (70) reported that they are involved in using diet diaries. GDPs appeared to target patients for dietary advice: GDPs reported they personally gave diet advice to an estimated 63% of their patients, and referred patients to DCPs for diet advice for 11% of their (GDPs') patients. GDPs used diet diaries more often for child than adult patients. Diet diaries usage was lower among younger dentists and in practices with higher percentages of NHS patients (p⟨0.05). Perceived insufficient remuneration for time involved in using diet diaries was the main reason given for their lack of use. CONCLUSION: Although recommended as best practice, most English GDPs do not frequently use diet diaries to collect diet information in dental practice, mainly due to perceived financial and time constraints. Development of a more efficient tool to assess the dietary habits of dental patients is needed.

Effect of gallium on growth of Streptococcus mutans NCTC 10449 and dental tissues.

Gallium-doped phosphate-based glasses (Ga-PBG) were assessed for their impact on Streptococcus mutans and dental mineralisation, firstly by disc diffusion assays followed by biofilms grown on nitrocellulose filter membrane (NFM) and constant-depth film fermentor (CDFF). Short-time exposure (10 min) effects of Ga-PBG on S. mutans biofilm were compared with that of 0.2% chlorhexidine. The effects of Ga-PBG on bovine enamel (which was investigated under pH-cycling condition) and dentine were analysed using transverse microradiography (TMR), profilometry and inductively coupled plasma optical-emission spectrometry (ICP-OES). The disc diffusion assays showed inhibition zones of 24.5 ± 0.5 mm for Ga-PBG compared with controls (C-PBG). Ga-PBG showed statistically significant growth inhibition of S. mutans biofilms on NFM (p = 0.001) and CDFF (p < 0.046) compared with hydroxyapatite (HA) and C-PBG. The CDFF assay revealed a maximum of 2.11 log colony-forming unit (CFU) reduction at 48 h, but short-time exposure effects were comparable with that of 0.2% chlorhexidine only on older biofilms (maximum of 0.59 vs. 0.69 log CFU reduction at 120 h). TMR analyses of the enamel revealed non-significant mineral loss (p = 0.37) only in the case of Ga-PBG samples compared with controls including sodium fluoride. ICP-OES analyses indicated transient gallium adsorption into dentine by calcium displacement. The results confirmed that gallium inhibited S. mutans growth and appears to have the potential to protect the enamel surface under conditions representative of the oral environment. Further work is needed to establish whether it has an application in daily oral hygiene procedures to prevent or reduce caries.

Reducing the variability between constant-depth film fermenter experiments when modelling oral biofilm.

AIMS: The inherent instabilities associated with the development of multispecies biofilm communities within the constant-depth film fermenter (CDFF) and other microcosm systems can yield unacceptable variability between experiments, which could limit their potential applications in oral microbiology. The extent of this variability needs to be determined and a protocol developed which minimizes it. METHODS AND RESULTS: Two custom-made CDFFs were supplied concurrently with the same inoculation culture, begat from an aliquot of a saliva pool and artificial saliva growth medium via a dual-channel pump. Transformed log(10) data of the viable counts at fixed time points were analysed using the Bland-Altman approach to test for the levels of agreement between two CDFFs running concurrently and those CDFFs run in series. The coefficients(95%) of agreement were lower (i.e. less variable) in the concurrent model than when run in series for total counts of bacteria (1.238 vs 2.124), Lactobacillus spp. (0.517 vs 1.431) and Mutans streptococci (2.817 vs 3.864). Other measures of variability showed a similar trend. CONCLUSIONS: Operating CDFFs concurrently minimizes the degree of difference and variability between them. SIGNIFICANCE AND IMPACT OF THE STUDY: Operating CDFFs concurrently will improve the sensitivity for experiments that seek to determine the effects of a variable, such as a nutritional supplement or antimicrobial agent, and a control.

Effect of post-brushing mouthwash solutions on salivary fluoride retention--study 2.

OBJECTIVE: This study evaluated the effects of three post-brushing mouthwashes containing 0 ppm F, 225 ppm F, and 500 ppm F, respectively, on salivary fluoride retention after brushing with 1450 ppm fluoride (as NaF) toothpaste and rinsing with water immediately after brushing. METHODS: In this three-phase, randomized, cross-over study, an ion-specific electrode was used to measure salivary F levels in thirty trial participants before brushing (Time 0), and after brushing, rinsing with water, and then rinsing with one of the three mouthwashes. Time points evaluated after brushing were one, three, five, 10, 20, 30, 45, and 60 minutes. For saliva sample collections, subjects were asked to pool saliva in their mouths for 10 seconds before spitting out into a container for each of the time points. RESULTS: The AUC0-60 means for F in saliva were 554, 252, and 20 for the 500, 225, and 0 ppm F mouthwash groups, respectively. The 500 ppm F mouthwash resulted in a 2660% increase in total fluoride salivary retention over 60 minutes when compared with the 0 ppm F group, and a 120% increase when compared with the 225 ppm F group. A significant difference (p < 0.001) in the AUC0-60 means between the three groups was observed using analysis of variance (ANOVA). Paired t-tests also showed significant differences in the mean fluoride retention over 60 minutes for all three pair-wise group comparisons (p < 0.001). CONCLUSION: Use of a fluoride mouthwash containing 225 ppm F or 500 ppm F produced a significant increase in salivary fluoride retention following brushing with a 1450 ppm F toothpaste and rinsing with water compared to rinsing without fluoride. The use of the 500 ppm F mouthwash may be of particular benefit to those at high caries risk.

Photobleaching of red fluorescence in oral biofilms.

BACKGROUND AND OBJECTIVE: Many species of oral bacteria can be induced to fluoresce due to the presence of endogenous porphyrins, a phenomenon that can be utilized to visualize and quantify dental plaque in the laboratory or clinical setting. However, an inevitable consequence of fluorescence is photobleaching, and the effects of this on longitudinal, quantitative analysis of dental plaque have yet to be ascertained. MATERIAL AND METHODS: Filter membrane biofilms were grown from salivary inocula or single species (Prevotella nigrescens and Prevotella intermedia). The mature biofilms were then examined in a custom-made lighting rig comprising 405 nm light-emitting diodes capable of delivering 220 W/m(2) at the sample, an appropriate filter and a digital camera; a set-up analogous to quantitative light-induced fluorescence digital. Longitudinal sets of images were captured and processed to assess the degradation in red fluorescence over time. RESULTS: Photobleaching was observed in all instances. The highest rates of photobleaching were observed immediately after initiation of illumination, specifically during the first minute. Relative rates of photobleaching during the first minute of exposure were 19.17, 13.72 and 3.43 arbitrary units/min for P. nigrescens biofilms, microcosm biofilm and P. intermedia biofilms, respectively. CONCLUSION: Photobleaching could be problematic when making quantitative measurements of porphyrin fluorescence in situ. Reducing both light levels and exposure time, in combination with increased camera sensitivity, should be the default approach when undertaking analyses by quantitative light-induced fluorescence digital.

Effects of zinc and fluoride on the remineralisation of artificial carious lesions under simulated plaque fluid conditions.

The aim was to study the effects of zinc (Zn) and fluoride (F) on remineralisation at plaque fluid concentrations. Artificial carious lesions were created in 2 acid-gel demineralising systems (initially infinitely undersaturated and partially saturated with respect to enamel) giving lesions with different mineral distribution characteristics (high and low R values, respectively) but similar integrated mineral loss values. Lesions of both types were assigned to 1 of 4 groups and remineralised for 5 days at 37°C. Zn and F were added, based on plaque fluid concentrations 1 h after application, to give 4 treatments: 231 µmol/l Zn, 10.5 µmol/l F, Zn/F combined and an unmodified control solution (non-F/non-Zn). Subsequently remineralisation was measured using microradiography. High-R lesions were analysed for calcium, phosphorus, F and Zn using electron probe micro-analysis. All lesions underwent statistically significant remineralisation. For low-R lesions, remineralisation was in the order F(a) < non-F/non-Zn(a) < Zn(a, b) < Zn/F(b), and for high-R lesions F(a) < non-F/non-Zn(b) < Zn(b) < Zn/F(c) (treatments with the same superscript letter not significantly different, at p < 0.05). Qualitatively, remineralisation occurred throughout non-F/non-Zn and Zn groups, predominantly at the surface zone (F) and within the lesion body (Zn/F). Electron probe micro-analysis revealed Zn in relatively large amounts in the outer regions (Zn, Zn/F). F was abundant not only at the surface (F), but also in the lesion body (Zn/F). Calcium:phosphate ratios were similar to hydroxyapatite (all). To conclude, under static remineralising conditions simulating plaque fluid, Zn/F treatment gave significantly greater remineralisation than did F treatment, possibly because Zn in the Zn/F group maintained greater surface zone porosity compared with F, facilitating greater lesion body remineralisation.

The evaluation of a novel method comparing quantitative light-induced fluorescence (QLF) with spectrophotometry to assess staining and bleaching of teeth.

This study reports the development and evaluation of a novel method using quantitative light-induced fluorescence (QLF), which enables its use for quantifying and assessing whole tooth surface staining and tooth whitening. The method was compared with a spectrophotometer to assess reliability. Two experimental phases, intrinsic stain formation and tooth whitening, were conducted in vitro on 16 extracted bovine teeth. Intrinsic stains were developed via access through lingual surfaces and root canals of these teeth using tea solution (2 g/100 ml, Marks and Spencer Extra Strong Tea, Marks and Spencer, London, UK) for 6 days. Stains were removed using 33% hydrogen peroxide (VWR Prolab, Leicestershire, UK) in cycles over 150 min. Stain development/whitening was monitored with QLF (Inspektor Research systems, Amsterdam, Netherlands) and spectrophotometry (Easy shade, Vita Zahnfabrik, Bad Säckingen, Germany). Parameters Delta F for QLF and Delta E for the spectrophotometer were obtained. The progression of stain intensity and removal observed by the methods were tested for correlation using Pearson's correlation coefficient. Intra-examiner reliability for each method was tested. QLF showed a high correlation with spectrophotometry for detecting and monitoring intrinsic tooth stain progression (Pearson coefficient r was -0.987 with correlation significant p < 0.0001). For stain removal, the Pearson coefficient (r) between both methods was -0.906 with no significance p = 0.094. The use of an external reference material in combination with the inner patch QLF analysis technique had the ability to detect and measure whole tooth surface staining and its removal longitudinally. The reliability of the method shows a potential clinical application.

The influence of varying fluoride concentrations on in vitro remineralisation of artificial dentinal lesions with differing lesion morphologies.

OBJECTIVE: The influence of low-level fluoride (F) concentrations and lesion characteristics on the remineralisation of sub-surface root caries was investigated in vitro. DESIGN: Experimentally produced dentinal carious lesions were exposed to artificial saliva in the presence of 0.00ppm, 0.48ppm, 2.49ppm or 4.91ppm F (as NaF) for 5 days. Calcium, phosphate and fluoride ion uptake was quantified by chemical assay. Baseline changes in the mineral content and distribution of the lesions were assessed by transverse microradiography (TMR). RESULTS: The uptake of calcium and phosphate was significantly increased (p<0.05) by fluoride, even at low concentrations. The action of fluoride was influenced by the mineral content and distribution of the lesions at baseline, however, with the location and degree of mineral deposition being strongly related to the mineral content of the lesions surface layer. CONCLUSIONS: The process of remineralisation of root dentine is multifactorial. The morphology of lesions at baseline significantly affected the location and quantity of mineral deposition.

The susceptibility of bleached enamel to staining as measured by Quantitative Light-induced Fluorescence (QLF).

OBJECTIVES: To report the use of Quantitative Light-induced Fluorescence (QLF) to determine if there was a tendency for bleached enamel to take up extrinsic stains more than unbleached enamel. METHODS: Bovine teeth devoid of stains were selected, the roots removed and enamel gently pumiced. Each tooth was sectioned into two and each half randomly assigned to two groups (bleached or unbleached). Windows were created on each half using clear acid resistant varnish. 38% Hydrogen peroxide gel was applied to the exposed windows of the bleached group for 1 hour. The teeth were rinsed and dried. Bleached and unbleached halves of the same teeth were then mounted on glass rods attached to pot lids using green stick. QLF images were taken. The teeth were subjected to a cycle of artificial saliva, chlorhexidine and tea (2 minutes in each solution). This was repeated 5 times. QLF images were taken at the end of each cycle. RESULTS: The uptake and progression of stain was detected in all the sections by QLF. Using paired t- test (SPSS) there was no significant difference between the two groups for the change from baseline to the final stain cycle (p > 0.05), however there was variability in stain uptake within the groups as the cycles progressed. CONCLUSION: Bleaching of enamel in vitro does not appear to increase the susceptibility of enamel to extrinsic staining.

The efficacy of techniques for the disinfection of artificial sub-surface dentinal caries lesions and their effect on demineralization and remineralization in vitro.

OBJECTIVES: The efficacy of three techniques for the disinfection of artificial sub-surface root caries lesions and their response to subsequent episodes of de- and remineralization was investigated quantitatively in vitro. METHODS: Sub-surface dentinal lesions (n=20), cut into four experimental blocks and deliberately contaminated with Streptococcus mutans, were subject to either steam autoclaving (121 degrees C, 5min), gamma irradiation (4100Gy), immersion in 0.1% (w/v) thymol-distilled water solution (24h) or reserved as a control. Next, the lesions were incubated aerobically in sterile nutrient broth for 24h at 37 degrees C and resultant cultures plated onto blood agar and neutralisation agar. Ten blocks from each experimental group were then immersed in an acidic buffer solution or exposed to artificial saliva for 5 days. Baseline changes in the mineral content and distribution of the lesions were assessed by transverse microradiography (TMR). RESULTS: Micro-organisms were recovered from each control block and one block treated by gamma irradiation. Steam autoclaving and immersion in a thymol solution significantly decreased (p<0.05) the amount of mineral lost from the body of lesions subject to a further acid challenge. Mineral ion uptake by lesions exposed to artificial saliva was significantly increased (p<0.05) through disinfection by steam autoclaving. CONCLUSIONS: Gamma irradiation proved the most acceptable method for the disinfection of sub-surface root dentine lesions having the least adverse effect on demineralization and remineralization.

A novel approach to study in situ enamel erosion and abrasion lesions.

OBJECTIVES: This study investigated previous hypotheses that the tongue can abrade acid softened/eroded enamel surfaces. METHODS: Twelve upper removable appliances each retaining 2 anterior and 2 posterior human enamel specimens were constructed. Each specimen was exposed to acid on both surfaces, but only one surface was allowed contact with the tongue. Therefore, 96 surfaces were assessed. Appliances were worn from 9.30 to 17.00 Monday to Friday for 22days. Acid eroded lesions were created by immersing the specimens for 5min in 50ml orange juice three times daily. Enamel loss was measured using Quantitative light- induced fluorescence (QLF) and Non- contact profilometry (NCLP) and the differences (D) between tongue (Dt) and palate facing (DP) surfaces determined. RESULTS: %ΔFD(t-p) from the two anterior specimens were greater than from those placed posteriorly with mean values of 15.9% (±9.1) and 14.4% (±8.4), 5.6% (±8.7) and 4.5% (±6.6) respectively. Similarly, NCLP data showed anterior specimens had greater differences for mean step height (MSH) between tongue- facing and the palate- facing (control) surfaces than posterior specimens. MSHD(t-p) values were 59.4µm (±30.3) for anterior tongue facing surfaces and 55.5µm (±29.4) for posterior palate facing surfaces. For the posterior specimens MSH was 48.1µm (±26.1) and 51.7µm (±30.4) respectively (p<0.05). CONCLUSION: The greater enamel surface loss of the anterior specimens demonstrates that abrasion by the tongue on acid softened/eroded enamel in situ is likely.

Comparison of quantitative light-induced fluorescence (QLF) and digital imaging applied for the detection and quantification of staining and stain removal on teeth.

OBJECTIVES: This study compares the use of QLF with digital imaging in the detection and quantification of the development and removal of stain on teeth. METHODS: Two experimental phases, tooth staining and tooth whitening, conducted in vitro on labial 12 mm(2) enamel windows made on ten extracted bovine teeth, developed stains in 6-min cycles (2 min in each solution) using artificial saliva, chlorhexidine and tea solutions and removed them using sodium perborate monohydrate in 2-min cycle monitored at the end of each cycle with QLF (Inspektor Research Systems, NL) and digital photography (Fuji, Japan). The stain values were quantified as DeltaQ derived from QLF and DeltaE from digital imaging. This was observed by the two methods correlated with Pearson correlation coefficient (r). Regression equations (R(2)) were also obtained. RESULTS: For both staining and stain removal there was a statistically significant (p<0.01) reverse correlation between DeltaQ values for QLF (r=-0.924, R(2)=85.4%) and DeltaE values for digital imaging (r=-0.994, R(2)=98.8%), respectively. CONCLUSION: QLF showed a high correlation with digital imaging as a technique for detecting and monitoring tooth stains and tooth whitening in vitro. The potential for QLF with further development as a tool for monitoring staining and whitening of teeth may be possible in vivo in addition to the diagnostic ability for caries detection.

Dental erosion: possible approaches to prevention and control.

OBJECTIVES: To discuss the key elements for establishment of a preventive programme for dental erosion. DATA AND SOURCES: The data discussed are primarily based on published scientific studies and reviews from case reports, clinical trials, epidemiological, cohort, animal, in vitro and in vivo studies. References have been traced manually or by MEDLINE. STUDY SELECTION: The aetiology, pathogenesis and modifying factors of dental erosion were reviewed. Strategies to either prevent the occurrence or limit the damage of dental erosion or protect the remaining tooth tissues from further erosive destruction were reviewed and discussed. These includes: (A) measures to (1) enhance remineralisation and acid resistance of enamel surface softened by erosive challenge, (2) reduce the erosive potential of acidic products, (3) enhance salivary flow, (4) protect and restore erosively damaged tooth, and (5) provide mechanical protection against erosive challenge. (B) Health education geared towards (1) diminution of frequency of intake of dietary acids, and (2) change of habits and lifestyles that predispose teeth to erosion development. CONCLUSIONS: It may be easier to gain patients' compliance with the advice that immediately following an acidic challenge, a remineralising agent, such as fluoride mouthrinses, fluoride tablets, fluoride lozenges or dairy milk, should be administered to enhance rapid remineralisation of the softened tooth surface as well as serve as a mouth refresher, or an alternative, a neutralising solution should be used. Effective counselling on erosion preventive regimes should involve all healthcare personnel, dentists, doctors, pharmacist, nurses/hygienists and clinical psychologists.

Caries and fluoride processes.

OBJECTIVES: The purpose of the work was to establish the level and source of salivary fluoride, whether it could interact with tooth mineral and whether it was able to effect calcium re-acquisition and remineralisation. METHODS: Fluoride in saliva and in solution was measured by electrode, calcium by complexometric titration and phosphate colourimetrically-to measure salivary fluoride, its uptake by mineral and the effects of such low levels on calcium and phosphate levels in solution in contact with suspensions of mineral hydroxyapatite. RESULTS: Fluoride levels in saliva were low but could interact with hydroxyapatite. Such levels caused apatite crystallite growth and preferential acquisition of calcium by calcium-deficient apatite. CONCLUSIONS: Salivary fluoride contents rose with increasing water fluoride levels. It was acquired by hydroxyapatite mineral. Topical fluoride was stored on oral tissues. Even these low fluoride contents could cause mineral crystallite growth with preferential calcium uptake. On a mineral area basis these effects were caused by quite low fluoride uptakes. These findings do not support reliance upon large fluoride uptakes by tooth enamel as evidence for commensurate caries reductions.

Development of an in situ root caries model. A. In vitro investigations.

OBJECTIVES: The paper describes preliminary in vitro investigations, the objectives of which were to examine the influence of certain experimental parameters on artificial carious lesion formation in root hard tissues, and their remineralisation. These experiments formed part of a wider study that aimed to develop an in situ model of root caries, based on the existing coronal caries model used in Liverpool. The present studies examined the effects (a) of the anatomical origin of the dentine, the presence or absence of cementum, the exposure time and the type of demineralising system, on lesion development, and (b) of baseline lesion size on the extent and location of mineral re-precipitation. METHODS: Mineral content parameters in plano-parallel sections taken from dentine lesions were determined by computer-controlled transverse microradiography. RESULTS: The importance of the anatomical origin of the dentine on lesion formation was investigated by comparing in vitro lesion formation in premolar and molar dentine, and in dentine from apical, middle and coronal thirds of the root: no difference was observed between these sites. Lesions formed more rapidly in acid buffer solutions than in acid gel systems, and were more reliably produced when cementum was removed. The effect of baseline lesion size on subsequent in vitro remineralisation demonstrated that a small baseline mineral content was associated with a larger percentage mineral gain. The location of mineral deposition throughout the lesion was also influenced by baseline mineral content parameters. CONCLUSIONS: The results form a basis for the further development of an in situ dentinal caries model, providing data to suggest that manipulation of parameters involved in the preparation of artificial carious lesions has a significant effect on the behaviour of the lesion, particularly the phenomenon of remineralisation. Further work is needed to investigate the behaviour of the model in situ.

Development of an in situ root caries model B. In situ investigations.

OBJECTIVES: The aims of this pilot study were to assess the suitability of an in situ model for root caries studies, and to investigate the effect of sub-surface lesion mineral content and ultrastructural organisation on remineralisation. METHODS: Subjects were selected by criteria generally used for coronal caries models. Plaque pH responses and salivary flow rates were determined by standard methods. The chosen substrate was human dentine with artificially induced caries-like demineralisation and sterilised by gamma-irradiation (4100 Gy). Two levels of baseline demineralisation were induced by exposure to an acid buffer for 2 or 5 days. Mineral content was measured by computer-controlled quantitative microradiography. RESULTS: Remineralisation in situ was greater in smaller lesions with lower surface mineral content than in larger lesions in which the surface mineral content was high. CONCLUSIONS: The model is suitable for further development for investigating dentinal caries. More work is needed to validate the model by means of a fluoride dose-response study.

Quantification of dental plaque in the research environment.

OBJECTIVES: To review the established and novel methods of plaque quantification employed in dental research, including a discussion of their merits and to present a new method of planimetrically measuring plaque using light induced fluorescence. METHOD: Quantitative light-fluorescence (QLF) images were acquired from the buccal surfaces of an individual who had refrained from oral hygiene both with and without traditional plaque disclosure. Digital photographs were also taken. Images were analysed using a novel method and a percentage plaque index produced. RESULTS: Traditional plaque indices are problematic due to their integral nature and their failure to detect small, but potentially clinically relevant changes in plaque area. The use of a fluorescent technique demonstrated good reliability although there was no correlation between red fluorescent plaque and total disclosed plaque suggesting that the auto-fluorescing plaque is not a good measure of total plaque volume. CONCLUSIONS: The use of planimetric techniques can increase the power of plaque studies, potentially reducing the number of subjects and time required to separate therapies or products. Fluorescent methods of quantification have potential as they enable clear separation of the plaque covered and non-covered tooth surfaces.

The use of in situ models and QLF for the study of coronal caries.

OBJECTIVES: The purpose of the paper is to review aspects of the systems available to model the caries process in enamel. METHODS: The in situ model developed in Liverpool, and the new method of quantifying mineral loss, Quantitative Light-induced Fluorescence (QLF), are described. QLF is a powerful new diagnostic tool which can be used to measure demineralisation and remineralisation in tooth surfaces in vivo; studies to optimise, validate and use QLF in different clinical situations are described. RESULTS: Examples of the use of in situ models show that they are particularly valuable for monitoring de and remineralisation of artificial lesions in relation to product testing as alternatives to clinical trials, and present significant advances over in vitro methods. Quantification of mineral loss by Transverse Microradiography (TMR) as in the traditional Liverpool model has produced much valuable information, but the destructive nature of the method limits experimental design, and removes the system from the clinical situation. As a possible alternative, QLF has been validated and optimised. Longitudinal measures can be made on the same surface, and examples of its use are for monitoring recurrent caries and demineralisation around orthodontic brackets. CONCLUSIONS: While current in situ models provide a major advance over earlier caries models, measurement of de and remineralisation by destructive methods such as transverse microradiography limits the design of experimental investigations. QLF offers significant time saving, reduces the cost of clinical studies, and because the measurements can be carried out longitudinally in vivo, can remove the need for intra-oral appliances carrying experimental tissues.

The effect of bleaching on enamel susceptibility to acid erosion and demineralisation.

INTRODUCTION: The purpose of this in vitro study was to determine if enamel that had been bleached by carbamide (urea) peroxide gel (CPG) was at increased risk of either acid erosion or demineralisation (early caries) than un-bleached enamel. METHODS: Human incisors were employed. The samples were randomly assigned to one of 4 groups; a) 10% CPG, b) 16% CPG, c) 22% CPG and d) 10% CPG with xylitol, fluoride and potassium. Each specimen was moistened with saliva and the appropriate formulation placed for 2 hours for a total of 40 hours of exposure. In order to ensure that bleaching had taken place, tooth shades were monitored using the Shade-Eye device. Following the bleaching process, one half of the specimen was subjected to an erosive challenge, the other to a demineralisation system with one half of each sub-sample retained as a non-bleached control. Samples were assessed longitudinally with quantitative light-induced fluorescence (QLF) and at the conclusion of the study with transverse micro-radiography (TMR). RESULTS: Erosion was detected in all samples (DeltaQ 126+/-23.4), in both bleached and non-bleached areas. There was no statistical difference between the bleached and non-bleached areas either within the treatment groups or between them. Caries-like lesions were detected on all samples; TMR revealed sub-surface lesions on all teeth and QLF data supported this (DeltaQ 89+/-18.9). Following statistical analysis there were no differences detected between the bleached and non-bleached areas, nor between the different concentrations of the bleaching solution. CONCLUSION: These results suggest that tooth bleaching with carbamide (urea) peroxide (using commercially available concentrations) does not increase the susceptibility of enamel to acid erosion or caries.

Plaque fluid as a bacterial milieu.

Studies of the extracellular, free concentrations of substrates, growth factors, inhibitors, and end-products of metabolism to which the intact plaque microflora is exposed in situ can assist in the understanding of factors controlling plaque pathogenicity. Information is becoming increasingly available from analysis of fluid separated by centrifugation of plaques collected at various intervals after an intra-oral pulse of dietary or experimental substrate, or different procedures or treatments having cariostatic potential. Such analytical results give more information than those obtained by analysis of aqueous or other extracts, because they yield values of substrate concentration representing those occurring at the bacterial cell surface. The largest body of information concerns extracellular levels of acid end-products of sugar catabolism in relation to food quality or sequence, and of amino acids and other products of nitrogen metabolism, in relation to studies of the detailed metabolic events of the Stephan curve, and of the demineralizing effect of the plaque environment. Areas where little information is available and which merit further study include plaque clearance of salivary and other components with anti-caries activity (e.g., antibodies, enzymes, fluorides, cations, other antimicrobials, etc.), and substrate concentrations to determine gradients for diffusion into and out of plaque.